A universal curve of apatite crystallinity for the assessment of bone integrity and preservation

Abstract

The reliable determination of bioapatite crystallinity is of great practical interest, as a proxy to the physico-chemical and microstructural properties, and ultimately, to the integrity of bone materials. Bioapatite crystallinity is used to diagnose pathologies in modern calcified tissues as well as to assess the preservation state of fossil bones. To date, infrared spectroscopy is one of the most applied techniques for bone characterisation and the derived infrared splitting factor (IRSF) has been widely used to practically assess bioapatite crystallinity. Here we thoroughly discuss and revise the use of the IRSF parameter and its meaning as a crystallinity indicator, based on extensive measurements of fresh and fossil bones, virtually covering the known range of crystallinity degree of bioapatite. A novel way to calculate and use the infrared peak width as a suitable measurement of true apatite crystallinity is proposed, and validated by combined measurement of the same samples through X-ray diffraction. The non-linear correlation between the infrared peak width and the derived ISRF is explained. As shown, the infrared peak width at 604 cm−1 can be effectively used to assess both the average crystallite size and structural carbonate content of bioapatite, thus establishing a universal calibration curve of practical use.

The Assessment of Bone Deterioration with Nuclear Magnetic Resonance Spectroscopy in a Multidisciplinary Context: The Case of the UNESCO World Heritage Site of Sedlec, Czechia

“…It must be also considered that linear correlations for FTIR‐ and XRPD‐derived indices, reflecting diagenetic paths, have been put into question (Dal Sasso et al . ). The issues include the following: sensitivity to chemical substitutions in apatite (Berna et al .…”

“…), effects of sample preparation (Trueman ) and the different methods adopted to retrieve parameters from the spectra (Dal Sasso et al . ).…”

“…Hitherto, no data on healthy human cortical bone are available; this information might be useful as a benchmark to estimate the extent of decay in archaeological material. It must be also considered that linear correlations for FTIR-and XRPD-derived indices, reflecting diagenetic paths, have been put into question (Dal Sasso et al 2018). The issues include the following: sensitivity to chemical substitutions in apatite (Berna et al 2004), band overlap (Grunenwald et al 2014), effects of sample preparation (Trueman 2013) and the different methods adopted to retrieve parameters from the spectra (Dal Sasso et al 2018).…”

Optimizing the biomimetic synthesis of hydroxyapatite for the consolidation of bone using diammonium phosphate, simulated body fluid, and gelatin

“…2a) [44,45]. On the other hand, the v 4 vibrational mode is typically observed as a resolved doublet, in which, the 'valley' between the doublet components (604 and 563 cm −1 , as seen in the same spectra), typically expressed as the infrared splitting factor (IRSF), is often used to assess the crystallinity of HAP [1, 13,25,34,[46][47][48][49]. In bone c-HAP, carbonates occur in two distinct types: type A for those replacing hydroxide ions of the stoichiometric HAP structure (with a maximum of their v 3 vibration at ~ 1456 cm −1 ), and type B for those replacing phosphates (at ~ 1415 cm −1 ) [31,40,[50][51][52][53] as seen in Fig.…”

“…Semi-quantification of carbonate in c-HAP can be achieved by calculating the carbonate index, i.e. the ratio of the type B carbonate absorption height over that of phosphate v 3 [49,54,55]. Also, an estimate of the type A/type B ratio can be obtained by comparing the areas under the deconvoluted components of the v 2 carbonate vibration at 880 cm −1 (type A) and 873 (type B) [21,56].…”